I see them in the classifieds on YTmag.com all the time. There are also several old engine groups on the internet that could steer you in the right direction. Around here, farm auctions are a good place to find one - sometimes fairly cheap.
Some old balers had a power unit on them, also old combines are a good source, no clutch on the combine units for the most part, they had an over center belt clutch like a gt.
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